This application claims priority under 35 U.S.C. xc2xa7xc2xa7119 and/or 365 to 97201947.5 filed in Europe on Jun. 25, 1997; the entire content of which is hereby incorporated by reference.
The present invention relates generally to wireless telecommunication system, and more specifically to master-slave filter tuning in a TDMA (Time Division Multiple Access) radio communication system.
In modern wireless telecommunication systems, such as the well-known cellular GSM (Global System for Mobile communications) and DECT (Digital Enhanced Cordless Telecommunication) telephone and data transmission systems, savings in component space, manufacturing costs and power consumption are important design issues.
In present DECT radio receivers, for example, the required selectivity is achieved by using a so-called SAW (Surface Acoustic Wave) band-pass filter. DECT is a Multi Carrier/Time Division Multiple Access/Time Division Duplex (MC/TDMA/TDD) digital radio access technique, having 10 radio carriers each provided 24 time slots, i.e. 12 receive and 12 transmit slots, serving 12 duplex communication channels, called a frame. The data and control bits are transmitted at a system clock frequency or system bit rate of 1152 kb/s.
At the receiving part of a typical double super-heterodyne DECT receiver, signals in the DECT frequency band (1880 to 1900 MHz) are down converted to a first IF (Intermediate Frequency) adapted for filtering of the down converted signal by the SAW-filter having a pass band of 1.152 MHz centered the first IF (typically 110 MHz). In a further conversion step the filtered signal is down converted to a second IF (typically 10 MHz) for further processing of the data.
SAW-filters have to be produced in a separate production process, resulting in a distinct (rather bulky) package. As a result, SAW-filters contribute significantly to the total costs, space and power requirements of a radio receiver.
Replacing SAW-filters by semi-conductor integrated filters, such as filters constructed from building blocks comprising transductor stages and capacitors, due to manufacturing process tolerances, up to 25% absolute difference in the actual and designed RC-product (Resistance times Capacitance value) of integrated components can occur.
To compensate for this huge error, the so-called master-slave tuning principle can be used, wherein the filter is made tunable to the correct or required operational characteristics. The tuning information is obtained from a tunable oscillator or resonator circuit. This oscillator or resonator circuit is built of the same building blocks as the filter and manufactured in the same production process (chip) like the filter.
By tuning the oscillator or resonator circuit to operate at its signal amplitude and frequency design values, the tuning signals can be also applied to tune the filter which, as a result, generally will operate within 1% of its design values. This accuracy is sufficient for most practical applications.
In normal operation, the receiver of a TDMA radio device is only operative during the receive time slot comprising signalling and information data for the device. In DECT, for example, for the activation of the receiver, a signal is available some 10 xcexcs before receiving the data. That is, the receiver circuitry has to be powered up and ready for receipt within the above 10 xcexcs interval. Accordingly, if the receiver circuitry can not be powered-up during this interval, the receiver should be powered-up for the complete receiving frame half, which is generally not acceptable in view of power consumption requirements.
Due to the relatively high quality (Q) factor of the oscillator or resonator circuit used in the master-slave filter configuration, for obtaining the required tuning accuracy, the time for powering-up the oscillator and its detection circuitry is relatively long. Without additional measures, the master-slave filter concept is in general not suitable for use in receivers of present TDMA radio communication devices.
In view of the above, it is an object of the present invention to provide a novel master-salve filter concept for use in TDMA radio receiver equipment meeting the power requirements as to the time of the operation and stand-by of a battery powered radio communication device, and such that SAW filters can be avoided.
It is a further object of the invention to provide such filter adapted for integration in an RF (Radio Frequency) analog ASIC (Application Specific Integrated Circuit) radio transceiver device providing the required selectivity, thereby effectively limiting the number of separate components of a PCB (Printed Circuit Board) and reducing the space requirements and weight of the radio equipment.
It is also an object of the invention to provide a radio communication unit for use in a cordless or cellular radio communication system comprising the novel filter concept.
These and other objects and features are achieved according to the present invention in a Time Division Multiple Access (TDMA) radio communication device arranged for receiving radio signalling and information data in receive time slots, comprising receiver circuitry having control means and filter means for the filtering of received radio signals. The filter means comprise a tunable filter part and a tunable oscillator or resonator part, operatively connected such that control signals operative for the tuning of the oscillator part are also operative for the tuning of the filter part, detector means for the detection of the oscillator operation, reference source means and comparator means, arranged to provide said tuning control signals from said detector means for the tuning of the oscillator to operate in accordance with the reference source means, and storage means for storing said tuning control signals if said filter means are made inoperative and for starting up said filter means by using said stored tuning control signals.
With the present invention a very fast start-up of the filter means can be achieved, because the tuning control signals are directly available from the storage means, thus avoiding the time required for the oscillator or resonator part to provide quasi-stable tuning control signals after powering-up.
In the concept according to the invention it is assumed that previously stored tuning control signals are still valid at a subsequent start-up of the filter means. This is a valid assumption in particular in a further embodiment of the invention in a TDMA radio communication device comprising timing and synchronisation control means, wherein under the control of said timing and synchronisation control means said tuning control signals are stored at the end of a receive time slot or slots in a frame and wherein said stored tuning control signals of said frame are enabled for starting up said filter means for the receipt of a receive time slot or slots of a subsequent frame.
In case of DECT, for example, the filter means according to the present invention can be ready for the receipt of a received time slot within the interval of 10 xcexcs, as described.
Preferably, the filter means, i.e. the filter part and oscillator or resonator part thereof, are digitally controllable means, whereas the storage means are arranged for storing tuning control signals in a digital format. Preferably, the digital storage means are of a type, which, if not operative, can be set in a low power consuming sleep mode. Accordingly, a further reduction of the power consumption is achieved resulting in longer operation time using the same battery.
In a yet further embodiment of the invention, the detector means comprise amplitude detector means and frequency detector means for the detection of the amplitude and frequency of the output signal of said oscillator part, said reference means being arranged for setting an amplitude and frequency of the oscillator output signal, and wherein said comparator means provide amplitude or quality (Q) tuning control signals and frequency tuning control signals for tuning said oscillator part and said filter part of said filter means.
The or each detector means, comparator means and reference source means, in a yet further embodiment of the invention, may comprise digitally operating means.
In the preferred embodiment of the invention, the filter part and oscillator part of the filter means comprise tunable transconductor transistor stages which are integrated in one and the same semi-conductor circuit during the same manufacturing process. As a result, instead of several space occupying components, a single component is achieved providing the required selectivity and operational characteristics for use in a receiver of, for example, the single super heterodyne type.
The master-slave filter tuning according to the invention is in particular suitable for use in a transceiver ASIC (Application Specific Integrated Circuit) arranged for use in TDMA radio transceiver means.
The invention relates further to a remote communication unit, such as a radio telephone for use in TDMA radio communication system, comprising transceiver means, timing and synchronisation control means, and information and signalling processing means, wherein the transceiver means comprise filter means according to the present invention.
The above-mentioned and other features and advantageous of the invention are illustrated in the following description with reference to the enclosed drawings.